1. Field of the Invention
This invention relates to a lid which can be inexpensively molded of polyethylene or other synthetic resin to receive a handle or the like. The invention also includes a process for making a lid with an opening extending generally transverse to the pull direction of the mold.
2. Description of the Prior Art
Injection molding of synthetic resins such as polyethylene has made possible the mass production of a variety of articles at a relatively inexpensive cost. The goal of the manufacturer is to produce a quality article at a minimum cost. Aside from material, some of the largest variable costs include labor and tooling.
The most inexpensive mold tooling are simple molds which merely pull apart after the molten polyethylene has been injected therein. These simple molds are generally not capable of producing articles which require holes or other cavities which are oriented transversely to the axis along which the two piece mold is pulled apart. Molded articles made from simple molds and having a transverse hole or cavity have been unable to release from the mold and/or provide a surface with sufficient strength in front of the cavity. As a result, it has heretofore been believed that it was not possible to successfully and commercially mold a lid which included creating an inwardly extending cavity.
Two approaches are generally used to make such holes or cavities. In either approach, the molding machine has included a first component for molding the exposed or top surface of the lid and a second component for molding the rough or bottom surface of the lid. For most lids this second component creates a lip or inwardly projecting thread. The first component of the mold must pull away freely from the lid, and the second component usually includes push pins which push against the lid to free it from the second component. Thus, as the mold separates, the first component pulls free of the lid while the pins associated with the second component push against the back surface of the lid to force the lid free and permit it to fall out of the mold.
In the first approach to creating a cavity extending transversely to the direction of separation of the mold components, a manufacturer may use a side-core pull mold. The side-core pull mold requires much more precision to manufacture and is not only much more expensive to manufacture (about 25 to 30%) but requires a much more expensive molding machine to operate than simple straight-pull molds. Side-pull cores also take up more space than simple molds and thus provide reduced production capacities. In addition, an operator must be continually in attendance because the side-core pull molds are more likely to malfunction which can quickly ruin the expensive mold.
One other way of obtaining holes or cavities which are transverse to the axis along which the mold is pulled apart is to use a simple mold but then drill the hole in the desired location and direction. This method requires the use of an additional operator to drill the holes or cavities and an additional piece of equipment which may cost ten to fifteen thousand dollars.
These additional costs have been particularly aggravating in the production of lids for sun tea jars. These are relatively low cost items but which preferably include a swingable handle so as to present a relatively flat top. A hole is typically provided by one of the two methods outlined above in order to receive the handle with enough strength to support the weight of the jar and its contents, which for a one-gallon jar would be about nine pounds. To provide a hole so that the lids can receive the handle has required the use of expensive side-core pull molds or an additional drilling station when simple straight-pull molds are used. In order to reduce costs, improve efficiency and free workers for more productive tasks, there has developed a need for a lid which includes a cavity capable of receiving a handle but which can be made in a simple mold.